Getting started with Express, Koa or hapi
Learn how to setup Defer and trigger your first background function.
Setup
Install the @defer/client
Create a defer/
folder
Defer expects to find all the background functions in the defer/
folder.
In an Express/Koa/hapi app, we recommend creating an src/defer/
folder as
follows:
- src/
- api.ts
+ - defer/
- .env.example
- package.json
- tsconfig.json
Important
All files inside the defer/
folder must be Background Functions (wrapped
with defer()
); any shared code (ex: utils) should be moved outside of the
defer/
folder.
The defer/
folder can be placed anywhere in your project and can contain
nested sub-folders.
Write a background function
A background function is a function equivalent to a background job.
All background functions must live in the defer/
folder.
Choose how to write your first background function:
Our background function is ready to be used; let’s see how to call it from your application.
Call your background function
Whenever you choose to use the helloWorld()
function or create your own, the
following example showcasing how to call helloWorld()
from a Express, Koa or
Hapi API route demonstrates how easily you can trigger a background function
execution.
import express from "express";
// we import our `helloWorld()` background function
import helloWorld from "../../defer/helloWorld";
const app = express();
const port = 3000;
app.get("/", async (req, res) => {
// calling a background function triggers an execution on Defer
await helloWorld("Charly");
res.send("Hello World!");
});
app.listen(port, () => {
console.log(`Example app listening on port ${port}`);
});
How does Defer work?
If you are wondering how calling a background function triggers an execution on Defer, please refer to this guide: How Defer works.
Once your new API route is defined, please commit and push it to your branch.
Now that your API contains a background function and an API route that calls it, let’s ensure that your Defer token is properly configured.
Setup your Node.js / Bun version
Node.js is the default runtime, and version 18.x
will be used if you don't
specify your own.
Node.js versions 18.x
and 20.x
are supported, and Bun versions
1.x
are supported.
To use Defer with Bun, you need the @defer/client
version to be >=1.11.0
To change your runtime and its version, edit the engines
field of your
package.json
:
For more details about the supported runtimes, like how dependencies are installed, check our Deploy section
Configure
Create your Defer application
First, sign in to the Defer Console, then, go to the "Setup application page."
Once your application is correctly configured, click the “Create” button.
You should land on the application's page with a build running; you can go to the Defer Console to check its status.
Your first successful build on the Defer Console
You can now get a Defer Token by navigating to the Settings page:
Copy your Defer token for the next step
Configure your API deployment
Your API deployment should expose your Defer Token as an environment variable in order to get your background function deferred when called.
Deploy
Now, with your API deployment containing your Defer Token and your project’s
builds ready on Defer, open your browser and test your /helloWorld
API route.
In the helloWorld()
background function scenario, visit the /
route.
You should see that your API answered quickly, and by going to your Defer Console, you should see that your background function has 1 execution running - or finished:
By clicking on see executions, you will access the executions list: